The present invention relates to a ground station comprising a plurality of directional antennas for a two-way ranging system which, after a fixed time following reception of a DME interrogation signal, radiates a DME reply signal approximately in the direction of arrival of the interrogation signal.
This ground station is suitable for the distance-measuring portion of the so-called DLS landing system, which is described in an article by M. Bohm and G. Peuker, "DLS-ein neues Anflugund Landesystem", Elektrisches Nachrichtenwesen, Vol. 50 (1975), No. 1, on pages 37-43 (particularly on p. 39).
A detailed description of a known DME system, which is also used for distance measurement in TACAN, is contained, for example, in an article by R. I. Colin and S. H. Dodington, "Principles of TACAN", Electrical Communication, Vol. 33, (1965), No. 1, on pages 11 to 25 (particularly in section 2.3).
Using prior art directional reception and directional radiation, errors caused by multipath propagation can be reduced. With directional radiation of the DME reply signal, however, it is a practical requirement that it shall be possible to receive at least 700 pulse pairs per second from all directions and this requirement is no longer fulfilled in prior art apparatus of the type. This number of pulses is necessary to derive (in the airborne equipment) a voltage for controlling receiver sensitivity.
An important specification to be met by DME equipment is contained in "International Standards and Recommended Practices, Aeronautical Telecommunications, Annex 10 to the Convention on International Civil Aviation (ICAO)", Section 3.5. The part essential applicable to the invention is contained in Section 3.5.3.1.5.4.